Dr. P. Lucas U of A MSE 110 Intro to thermo •F i rs t l a w : ∆E = Q + W∆ E = Q - P ∆V The internal energy of a system can only be changed through transfer of heat or work from the surrounding. This implies conservation of energy. Energy is neither created nor destroyed, it is only transferred. • For a heat transfer at constant V: ∆ E = Q V• Enthalpy : H = E + PV• For a heat transfer at constant P: ∆ H = Q PThe enthalpy change ∆ H correspond to the heat transferred during a reaction at constant P, which is the case of most practical reaction. ∆H = ∆ E + P∆ V The total heat ∆ H absorbed at constant P is mostly used to increase the internal energy E of the system (kinetic and potential energy of the molecules) and a small part is used to push back against the ambient pressure (P ∆ V).• Heat capacity : The heat capacity defines the T change of a material for a given heat transfer. • The isothermal enthalpy change during a phase transition correspond to a peak in Cp which is used to detect transition temperature experimentally. SUMMARY FROM LAST CLASS P P dT dH C       = V V dT dE C 

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